I had the opportunity to play with the S390 and Panasonic BDT320 last night. From my understanding, both players should be representative of the PQ and AQ from the S590 & S790 and BDT120 & BDT220 respectively, as these other models only add/subtract various optional features and settings - none of which affect the default playback quality. My impressions from viewing on my new 82" DLP:
Build Quality - Both the Sony and Panasonic felt fairly cheap and plastic-y to me. The Panasonic did feel a little better, but that is likely because I was comparing Sony's lowest-end to Panasonic's current highest-end. The Panasonic was also abnormally long for a player, which made it awkward to find a spot in my entertainment center. Ultimately, the build quality is of minimal concern to me, as it will remain on a shelf until the day I retire it. I do wish the S390 had a front display, however this feature is available on the S590 and S790.
Remote - Jesus Christ, Panasonic - what was the idea here? I'm a gadget guru and play with laptops and smart phones all day, but this touchpad remote had me baffled. Luckily, I was able to use an older Panasonic remote I had lying around (they also have a smart phone app). Thankfully, the 220 comes with a normal remote. The Sony remote did its job admirably enough, no complaints. I definitely preferred the Sony remote, and a smart phone media remote is available for it as well.
Interface - I was pleased with both the Panasonic and Sony UI. I give the slight edge to the Sony, but probably because I'm more familiar with it from the PS3. I think most folks would be happy with either. The Sony just seemed more intuitive to me from previous personal experience.
Disc Loading Time - The Panasonic was faster with just about everything. I did not break out a stopwatch, so I can only tell you it was quicker - but not by how much. I didn't spend much time evaluating this, as I'm typically grabbing snacks and blankets and getting settled while the disc is loading anyway. My old BD35 took forever and a day, yet it never really bothered me. The Sony was no slouch, but it was slower.
DVD Playback - Both players did an excellent job and I would be hard pressed to choose one over the other. The Panasonic had more tweaks to the picture available, if that's your sort of thing. I usually disable just about every "enhancement", so they didn't factor into my observations. I did not have these players showing side-by-side, so there could be some subtle differences, but I would be more than happy with either player. I still buy quite a few used DVDs (they're so hard to turn down at $2-$3 a pop), so this is great news. I have not used an Oppo, so I could not tell you how the picture compares. I do find it hard to believe that standard DVD could look any better than it does here.
Blu-ray Playback - No discernible differences. Aside from the aforementioned load times, I could not tell you which player was which.
Network/Online Features - The Sony wins here for functionality and sheer number of online apps. The Netflix interface was especially quick on the Sony compared to the sluggish version on the Panasonic. Both players were able to eventually get to the movie just fine, but it seemed like a much smoother process on the Sony. My brief experiment with DLNA proved to benefit the Sony as well, though the Panasonic worked fine with some content. I would pick up the Sony if DLNA was a priority, as it seemed to play more formats with less of a hassle.
3D Playback - I did not evaluate, as I don't care for 3D content. Mileage may vary, so see other reviews.
If I had to choose a single player between the two, it would be the S390. While the 320 is a fine player, it just didn't seem to "run on all cylinders" as smoothly as the Sony did for my needs. Each has their pros and cons, so you'll want to evaluate your priorities. They're so close, each could be a winner based on your needs.
Given the negligible price difference online with the S390, I'm inclined to pick up a S590 for the addition of a front display (and the option of 3D if some must-see exclusive comes out one day).